Humira is a human antibody (protein) that binds with human TNF, inactivating the TNF and hence partially dampening the immune system.
This antibody was produced by what is called a "phage display" - a very high tech biotechnology method where, in this case, the human DNA that codes for the antibody protein and a lot of other proteins was inserted into the DNA of a type of virus called a bacteriophage. This enabled several selection steps that allowed the gene to be identified and isolated for further use.
Once identified the DNA was used to infect bacteria, which in turn were "tricked" to make copious amounts of the ant-TNF proteins which could assembled then be purified into useable drug.
This is a very simplified description of some very clever, highly complex, very cool biotechnology. So don't feel like a "nitwit" for not immediately understanding it.